Art of vulcanizing or curing caoutchouc substances



Patented July 7, 1925.

UNITED STATES.

PATENT OFFICE.

LORIN B. sEBRE'LI. AND CLAYTON w. BEDFORD, or AKRON, OHIO, ASSIGNORS TO THE GOODYEAR TIRE & RUBBER COMPANY, or AKRON, OHIO, A CORPORATION or OHIO.

ART OF VULCANIZING OB CURING CAOUTCHOUC SUBSTANCES.

No Drawing. Original application filed December 7, 1921, Serial No. 520,689. Divided and this application filed November 30, 1928.

To all whom it may concern:

Be it known that we, LORIN B. SEBRELL and CLAYTON W. BEDFORD, citizens of the United States, and residents of Akron, Ohio, have invented new and useful Imcirovements in the Art of Vulcanizing or uring Caoutchouc Substances, of which the following is a specification, this application being a division of application Serial Number 520,689. a

Our invention relates to accelerators of the vulcanization of rubber and it has, for

I mix and subjected to the heat of vulcani- I its primary object, the provision of accelerators of high curing i power, which may be prepared in a manner best adapted to facilitate their production.

In Patents Numbers 1,371,662; 1,371,663 and 1,371,664, issued March 15, 1921, a number of accelerating reagents are described as the reaction products of sulfur and nitrogen-containing bodies. In this application it is our desire to set forth specific ingredients, Or reagents, which are especially active accelerators and which result from reactions of sulfur with thiocarbanilid. As set forth in the above mentioned patents, accelerators of considerable commercialvalue may be prepared by effecting certain reactions, such as the reaction of sulfur with thiocarbanilid, befbre the chemicals are incorporated in the rubber zation. By establishing proper conditions of temperature and admixture of the reacting materials, a satisfactory accelerator is assured, whereas during vulcanization, such ideal conditions might not obtain. I

By our present invention we disclose the specific reaction roducts which are responsible for the big curing power of the reaction products of sulfur with thiocarbanilid. The, desired accelerators may, consequently, be more efliciently produced and utilized to best advantage, by their isolation and use in pure or semi-pure state.

Serial No. 677 ,877.

Jacobson and Frankerbaker, Ber. 24',

1400 (1891), and others, have described mercaptobenzothiazol as the sulfur reaction product of phenyl mustard oil ON=C=S.

It is also well known that thiocarbanilid form benzothiazyl-disulfide,

i l ja -SK which in turn dissolves sulfur'to form polysulfides, the probable formula of wh ch 1s as follows:

Extensive experiments have definitely established that the free .mercaptan, its

normal or basic lead or zine salts, its disulfi'de or disulfide polysultide are all desirable accelerators for the vulcanization of rubber by sulfur. Furthermore, depending upon the rubber compound in which they are to be utilized, they may be isolated and employed in a pure or nearly pure condition. The reaction products of thiocarbanilid and sulfur may be separated from aniline before their use, or they may be utilized without isolating any of the resulting constituents.

It has also been determined that mercaptobenzothiazol will react further with sulfur and that a. second substitution of sulfur in the nucleus may occur. If this sulfuration process is not permitted to proceed too far, an accelerator of high power may still be obtained.

In order to illustrate the merits of accelerators prepared in accordance with our invention, we have vulcanized rubber under different degrees of steam pressure and tested the physical properties'of the resulting products. In addition to comparing the accelerators with each other, such tests prove the desirability of such accelerators with respect to similar reagents known to those familiar with the art.

In the following chart is shown the time required to cure rubber at 20 pounds and 40 pounds of steam pressure. Although the usual curing ten'iperature adopted is represented by 40 pounds steam pressure, the lower steam pressure was also utilized because the trend of present day practice is to reduce the temperature.

In the following examples a mixture was utilized which consisted of:

Smoked sheet, 100 parts; zinc oxide, 5 parts; sulfur, 3.5 parts. One part of mercaptobenzothiazol was used and equivalent proportions of its derivatives to correspond to one molar weight of the original mercaptan.

Maximum tensile Load to give 700% Optlmum cure strength elongation Steam pressure 20 lbs. 40 lbs. 20 lbs. 40 lbs. 20 lbs. 40 lbs.

I hrs. min. hrs. min. kgJcmJ kmlcm Ice/rm. kgJcm 2 Mercaptobenzothiszol 30 0 30 210 160 1L0 Zinc salt of mercaptobenzothiazoL 1 00 0 15 240 210 220 210 Lead salt of mercaptoben'zothlazol. 1 00 0 15 210 190 210 190 BenZOthiaZyl-disnlfidn 1 30 0 30 130 170 150 110 The fact that the above accelerators may be isolated from the reaction products of softening action of the thioanilines which otherwise are present.

Although we have specifically described accelerators that may be utilized in promoting the vulcanization of rubber and stated our theories with regard thereto, it is obvious that minor changes may be made in the application of the principles of our invention Without departing from the spirit and scope thereof and We desire, therefore, that only such limitations shall be imposed as are indicated in the appended claims.

lVhat we claim is:

l. A method of vulcanizing eaoutchouc which comprises admixing caoutchouc and a vulcanizing agent with a lead salt of mercaptobenzothlazol and vulcanlzln 2. A method of vulcanizing caoutchouc which comprises admixing caoutchouc and a vulcanizing agent with a basic lead salt of mercaptobenzothiazol and vulcanizing.

3. The vulcanized caoutchoue product formed by the reaction of caoutchouc, a vulcanizing agent and a lead salt of mercaptobenzothiazol. I I

4. The vulcanized caoutchouc product. formed by the reaction of eaoutchouc, a vulcanizing agent and a basic lead salt of mercaptobenzothiazol.

In witness whereof we have hereunto signed our names in the presence of two subscribing witnesses.

LORIN B. SEBRELL. CLAYTON W. BEDFORD.

lVitnesses O. E. BEE, F. A. Lmn. 

